1=pod 2 3=head1 NAME 4 5EVP_PKEY_derive_init, EVP_PKEY_derive_init_ex, 6EVP_PKEY_derive_set_peer_ex, EVP_PKEY_derive_set_peer, EVP_PKEY_derive 7- derive public key algorithm shared secret 8 9=head1 SYNOPSIS 10 11 #include <openssl/evp.h> 12 13 int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx); 14 int EVP_PKEY_derive_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]); 15 int EVP_PKEY_derive_set_peer_ex(EVP_PKEY_CTX *ctx, EVP_PKEY *peer, 16 int validate_peer); 17 int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer); 18 int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen); 19 20=head1 DESCRIPTION 21 22EVP_PKEY_derive_init() initializes a public key algorithm context I<ctx> for 23shared secret derivation using the algorithm given when the context was created 24using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to 25fetch a B<EVP_KEYEXCH> method implicitly, see L<provider(7)/Implicit fetch> for 26more information about implicit fetches. 27 28EVP_PKEY_derive_init_ex() is the same as EVP_PKEY_derive_init() but additionally 29sets the passed parameters I<params> on the context before returning. 30 31EVP_PKEY_derive_set_peer_ex() sets the peer key: this will normally 32be a public key. The I<validate_peer> will validate the public key if this value 33is non zero. 34 35EVP_PKEY_derive_set_peer() is similar to EVP_PKEY_derive_set_peer_ex() with 36I<validate_peer> set to 1. 37 38EVP_PKEY_derive() derives a shared secret using I<ctx>. 39If I<key> is NULL then the maximum size of the output buffer is written to the 40I<keylen> parameter. If I<key> is not NULL then before the call the I<keylen> 41parameter should contain the length of the I<key> buffer, if the call is 42successful the shared secret is written to I<key> and the amount of data 43written to I<keylen>. 44 45=head1 NOTES 46 47After the call to EVP_PKEY_derive_init(), algorithm 48specific control operations can be performed to set any appropriate parameters 49for the operation. 50 51The function EVP_PKEY_derive() can be called more than once on the same 52context if several operations are performed using the same parameters. 53 54=head1 RETURN VALUES 55 56EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1 57for success and 0 or a negative value for failure. 58In particular a return value of -2 indicates the operation is not supported by 59the public key algorithm. 60 61=head1 EXAMPLES 62 63Derive shared secret (for example DH or EC keys): 64 65 #include <openssl/evp.h> 66 #include <openssl/rsa.h> 67 68 EVP_PKEY_CTX *ctx; 69 ENGINE *eng; 70 unsigned char *skey; 71 size_t skeylen; 72 EVP_PKEY *pkey, *peerkey; 73 /* NB: assumes pkey, eng, peerkey have been already set up */ 74 75 ctx = EVP_PKEY_CTX_new(pkey, eng); 76 if (!ctx) 77 /* Error occurred */ 78 if (EVP_PKEY_derive_init(ctx) <= 0) 79 /* Error */ 80 if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0) 81 /* Error */ 82 83 /* Determine buffer length */ 84 if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0) 85 /* Error */ 86 87 skey = OPENSSL_malloc(skeylen); 88 89 if (!skey) 90 /* malloc failure */ 91 92 if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0) 93 /* Error */ 94 95 /* Shared secret is skey bytes written to buffer skey */ 96 97=head1 SEE ALSO 98 99L<EVP_PKEY_CTX_new(3)>, 100L<EVP_PKEY_encrypt(3)>, 101L<EVP_PKEY_decrypt(3)>, 102L<EVP_PKEY_sign(3)>, 103L<EVP_PKEY_verify(3)>, 104L<EVP_PKEY_verify_recover(3)>, 105L<EVP_KEYEXCH_fetch(3)> 106 107=head1 HISTORY 108 109The EVP_PKEY_derive_init(), EVP_PKEY_derive_set_peer() and EVP_PKEY_derive() 110functions were originally added in OpenSSL 1.0.0. 111 112The EVP_PKEY_derive_init_ex() and EVP_PKEY_derive_set_peer_ex() functions were 113added in OpenSSL 3.0. 114 115=head1 COPYRIGHT 116 117Copyright 2006-2023 The OpenSSL Project Authors. All Rights Reserved. 118 119Licensed under the Apache License 2.0 (the "License"). You may not use 120this file except in compliance with the License. You can obtain a copy 121in the file LICENSE in the source distribution or at 122L<https://www.openssl.org/source/license.html>. 123 124=cut 125